Cobalt-based alloys, such as Stellite® (Trade Mark for Co—Cr—W alloys) are hard alloys that are extremely resistant to many forms of wear. Products of these alloys show high hardness over a wide temperature range and are resistant towards corrosion. These products are used for inter alia casting of various kinds of components such as machine parts (bearing shells, valve seat inserts etc) or other components where high density, high strength and wear resistance are required.
Cast material often suffers from micro structural defects and carbide segregation. Carbide segregation leads to inhomogenously distributed hard phases. Disadvantages with such materials are lack of fracture toughness and poor machinability.
Powder metallurgy (PM) products generally possess a more homogenous microstructure than cast products. Further advantages with the PM production method are that costly machining into final shape may be excluded or minimized in comparison with traditional casting methods and that the method is more suitable for producing large quantities of small articles.
Attempts have been made over the years to produce cobalt-based products using the PM technology. Thus U.S. Pat. No. 4,129,444 discloses a process wherein atomised Co-based alloy powders are coated with a binder and then consolidated to produce discrete bodies that are dried, crushed and screened to obtain agglomerates. The agglomerates are pressed into green compacts which are sintered at high temperature. Furthermore the U.S. Pat. No. 5,462,575 discloses a powder metallurgy component prepared of a gas atomised Co—Cr—Mo alloy powder. The alloy powder is filled in a canister and baked in vacuum to degas the powder and the powder filled canister is thereafter consolidated, preferably by hot isostatic pressing (HIP).